This invention relates generally to threaded fasteners such as nuts and bolts and more particularly to threaded fasteners having an improved thread and reduced tolerances and improved fastening.
Threaded fasteners are well known to the art. One goal of threaded fasteners, particularly nut and bolt combinations, is to provide such a fastener that stays tightened and does not loosen in use. Generally accepted matching techniques result in tolerances between the nut an bolt threads and there is clearance or play which allows for movement between the elements. For example, a fastener or nut and bolt can loosen under load or vibration.
There are several prior art systems that try to remedy this problem. First, locknuts are used with a nylon washer locked in at the end of the nut. When the nylon washer contacts the bolt, it tightens around the thread and locks the nut in position. Locknuts have disadvantages. The nylon portion of nut has no load carrying threads. Further, it requires more material to make the nut longer and the nylon washer and the nut must be made separately and then crimped together. The locknut of this type can be used only a few times, is not as resistant to heat and requires chemicals i.e. nylon.
Deformed nuts have been used to overcome the loosening problem. These comprise nuts that are deformed out of the circular shape and made into rounded-off triangle shape. Then the bolt engages the threads, it contacts three points and the nut locks around the bolt. However, only heat-treated nuts can be used. To make the deliberate deformation requires an expensive manufacturing set-up. Further, the process is very slow. Also, the reaction of each individual nut is variable, which makes it difficult to predict or guarantee tolerances. Moreover, it can only be used with nuts.
A spiral lock is a lock thread is a commercially available alternative. However, the spiral lock provides an interference on the outside diameter of the bolt. It is difficult to control the interference with accuracy. The surface of the bolt thread can cause galling of the nut and subsequent failure.
Interference-fit threads are used which include a complete interference of the matching parts at the flanks to provide an interference or metal flow. However, based upon accepted machining practices, it is very difficult to produce, for example, class 5 threads (Federal Standard Screw-Thread Standards For Federal Services-Class 5 Interference Fit Screw Threads).
Examples of prior art fastener technologies are disclosed in the following U.S. patents: U.S. Pat. No. 1,369,156, to Woodward; No. 2,842,180, to Brown et al; No. 3,459,250 to Tabor; No. 3,661,194, MacFarlane et al.; No. 3,721,283, to Evan; No. 3,850,215, to Orlomoski; No. 3,927,503, to Wilson; No. 4,023,914, Holmes; No. 4,071,067, to Goldby; No. 4,396,321, Holmes; No. 4,846,614, to Steinbock; and No. 5,194,214, to Snyder et al.
It would be advantageous, therefore, to develop a fastener that has close tolerances yet is resistant to loosening or play without the disadvantages of the prior art designs.